1. Field of the Invention
This invention relates to the field of gear shift mechanisms for a manual automotive transmission and, more particularly, pertains to such mechanisms for preventing inadvertent engagement of the reverse gear.
2. Description of the Prior Art
German patent application DE-OS No. 19 11 206 describes a gear selector mechanism in common use in automotive vehicles. The gear selector lever is required to be raised or depressed against the force of a spring in order to Permit engagement of the reverse gear. However, because the gear selector lever in a five speed transmission is moved to the same shift channel when selecting the fifth forward speed ratio as when selecting the reverse gear, it has been found that a spring-loaded gear shift lock of the type described in that patent application is not entirely satisfactorily.
A gear shift mechanism that provides a reverse gear lock in a multiple speed transmission in which the fifth forward gear position lies in the same gear shift channel as the reverse gear position is described in German patent application DE-0S No. 30 03 079. There a rotatable locking cam, which is rotated in the vicinity of the shift lever support or in the gearbox extension near the end of the selector shaft, cooperates with a component of the shift lever or shift shaft to prevent direct engagement of the reverse gear while changing the position of the selector shaft from the forward gear position.
Gear shift reverse locking mechanisms known from the prior art have the disadvantage that troublesome dimensional tolerances can accumulate and affect adversely the cooperative relationship among the locking cams, latches, shift levers and the selector shaft.
German patent DE-OS No. 30 16 909 describes another gear shift locking mechanism for the reverse gear ratio in which a locking disc, located on the end of the selector shaft adjacent a shift finger, cooperates with the spring-loaded locking pin located in the transmission casing. The gear shift lock mechanism avoids a portion of the dimensional tolerance accumulation, but another portion is inherent in the design because certain parts of the mechanism are mounted on the selector shaft and other components are located in the casing.
According to the present invention, there is provided a gear shift mechanism that includes a lock or latch for preventing inadvertent engagement of the reverse gear for use in a manual transmission having multiple forward speed ratios. The mechanism includes a selector shaft, which is rotatable by means of a gear selector lever for selecting various gear shift channels and is axially displaceable by the gear selector lever for producing engagement of the selected gear ratio. The selector shaft carries a shift finger, engageable with shift forks in the respective gear shift channels, and an additional finger, which moves within a system of intersecting slots formed in a gate plate that defines the range of movement of the selector shaft. A pawl is rotatably mounted on the additional finger and is held by a spring-biased detent in one of two stable angular positions, one position aligned with, and the other perpendicular to, the gear shift slots or channels on the lock plate. A stop and at least one control pin are located on the gate plate to cooperate with the pawl. The control pin changes the angular position of the pawl relative to the gear shifting channels as the additional finger is moved by the vehicle operator relative to the gate plate while selecting the various gear ratios. The stop prevents engagement of the reverse gear when the pawl is turned by contact with a control pin to one of its stable angular positions.
The gear shift mechanism according to this invention is easy to assemble, operates reliably and requires components that can be manufactured easily and at low cost.